1. Technical Field of the Invention
The present invention relates to mobility management within a fixed communications system.
2. Description of Related Art
The re-directing of a call to a user-specified telephone, whether fixed or mobile, is known as call-forwarding. Call-forwarding is especially useful when trying to contact a user who is on the move in a fixed telephone network, where telephones, rather than people, are ascribed numbers. In one example, the user is given a “personal” telephone number. The user directs the network to forward all calls made to the personal number to a particular fixed telephone (the “borrowed” telephone). When the user moves, the user instructs the network to forward calls to a new fixed telephone. An example of a call-forwarding service in the United Kingdom is British Telecommunications plc's Flexinumber™ service. Not only can this service be used to forward calls within the UK, but it can be used to forward calls to another network located in another country such as the United States of America.
However, personal numbering has several limitations. Firstly, the personal number can only be used to receive calls. The user must make other arrangements if he wishes to make calls and does not want to burden the owner of the “borrowed” telephone with the cost of his calls. To provide full mobility, the personal number must allow the user to make calls from a “borrowed” telephone and for the calls to be charged to the personal number account. Secondly, the user is always tied to his home network. The user may, temporarily, want to use the services provided by a foreign service provider, in a foreign network, as if he were a subscriber to the foreign service provider.
Such facilities are, of course commonplace in cellular telephony systems such as GSM (Global System for Mobile Communications), in which the user takes the telephone terminal equipment (the handset) with him and the handset and network are designed to allow automatic registration of the handset with a local node (“base station”) of the network, as is well known in the art. However, in this case the user identity is associated with the termination equipment itself. Similarly, in the “Mobile IP” (internet protocol used to connect a terminal to the internet, the terminal itself identifies the user.